JPS61245511A - Dc and ac current transformer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial use portion) The present invention relates to a current transformer for direct current and alternating current.

(Prior art) A core having an air gap and supporting two windings,
An element that senses a magnetic field across the air gap and provides an electrical signal in response to this magnetic field, and is controlled by this electrical signal to feed one of the two windings in a direction that attempts to eliminate the magnetic field that generated this electrical signal. Current transformers for direct and alternating current are already known, which consist of a magnetic circuit consisting of an amplifier and a current measuring device connected in series with a winding supplied by this amplifier.

Current transformers of this type give completely satisfactory results for measurements of direct current and of relatively low frequency alternating current. However, as the frequency of the alternating current increases, the responsiveness of the system decreases, primarily on the one hand due to leakage flux due to the air gap and on the other hand as a function of the frequency response of the amplifier.

(Objective and Structure of the Invention) An object of the present invention is to improve the dynamic performance of the current transformer as described above. This object is achieved in that the magnetic circuit comprises a second ferromagnetic core without an air gap, which second core is magnetically coupled to the first core by the above-mentioned windings.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate a known device and an embodiment of the device achieving the objects of the invention, and will be described in detail below with reference to the drawings.

EXAMPLE In the known device shown in FIG. 1, the current transformer consists of a rectangular ferromagnetic core 1. The core 1 has an air gap 2 in which an element 3 is arranged to sense the magnetic field across the air gap. Element 3 can in particular be constituted by a Hall effect cell.

This cell consists of two cells arranged in series and whose connection point is grounded.
It is powered by current supplied by two batteries 4.5. When the cell 3 is placed in a magnetic field across its face, it produces a voltage between the two electrodes 6 and 7 placed at right angles to the flowing current. This voltage is applied to a very high gain amplifier 8 whose output is fed to a secondary winding 9 surrounding the core 1. In the drawing, for clarity, the winding 9 is shown wrapped around a branch separate from the branch containing the cell 3, but normally this secondary winding would be arranged in the same branch as the cell 3.

As soon as a magnetic field acts on the cell 3, the amplifier produces a current in the winding 9 which cancels out this magnetic field.

This magnetic field is generated by the passage of current through a primary winding 10, which often consists of a single straight conductor, producing the voltages mentioned above. The current flowing through the secondary winding 9 is measured by an ammeter A which gives an indication proportional to the current flowing through the primary winding 10.

Three operating states are recognized. These conditions are schematically shown in FIG.

a) The Shizugu Matahoyamo one state, fo”'L: In this state, the amplifier requires the basic relationship of a one-to-one current transformer, which is also applicable to direct current. The magnetic flux is zero and the amperage of the secondary winding is equal to the amperage of the primary winding.

b) Transient state, f, ~f3 limited by poles P1 and P2
: The interval 1) to flI depends on the frequency gain transient characteristics of the amplifier. The interval f2-f3 is characterized by a reduction in the level of the secondary signal at low frequencies due to the presence of an air gap.

C) Dynamic state, fs~fX+: The device acts as a current transformer.

FIG. 2 schematically depicts one embodiment of a current transformer that can significantly improve dynamic performance. For this improvement, the present current transformer has two ring-shaped magnetic cores arranged side by side 1). It is equipped with 12. The core 1) has an air gap 13 in which the first
A Hall effect cell similar to element 3 in the figure is arranged.

This cell is powered by a battery 4.5, the output of which drives a high gain amplifier 8. The core 12 is spaced from the core 1) by a distance sufficient to prevent magnetic shorting of the magnetic field in the air gear 13.

The ferromagnetic core 12 has no air gap and is dimensioned to provide accurate response in the range from frequencies below fl to frequencies fx2.

In short, the pole point P2 corresponding to the lower cutoff frequency of the current transformer itself formed by the ferromagnetic core 12 and the winding is
It is located at a frequency lower than the pole point P1 corresponding to the cut-off frequency of the amplifier. Therefore, the cutoff frequency of the device is linear from fo to fX2, which is higher than the frequency of the known device.

Of course, many alternative embodiments are possible.

For example, in practice, the ferromagnetic cores do not necessarily have to be rectangular or juxtaposed. - In a variant, one core can be placed inside the other, resulting in a compact design. The magnetic circuit 12 can also be constructed of two ferromagnetic cores arranged coaxially and provided on both sides of the core 1) with an air gap.

[Brief explanation of drawings]

FIG. 1 shows a known device. FIG. 2 shows an embodiment of the invention. FIG. 3 is a response curve diagram of the current transformer of FIG. FIG. 4 is a response curve diagram of the current transformer of FIG. 3... Sensing element, 8... Amplifier, 1)... First ferromagnetic core, 12... Second ferromagnetic core, 13...
Air gap, A... Current measuring device.

Claims (3)

[Claims] (1) A ferromagnetic core that has an air gap and supports two windings, an element that senses the magnetic field that crosses the air gap and provides an electric signal in response to this magnetic field, and a device that is controlled by this electric signal and that It consists of a magnetic circuit consisting of an amplifier that feeds one of the two windings in a direction that seeks to eliminate the magnetic field that generated the electrical signal, and a current measuring device connected in series with the winding that is fed by this amplifier. In a current transformer for direct current and alternating current, the magnetic circuit includes a second ferromagnetic core having no air gap, and the second ferromagnetic core is magnetically connected to the first ferromagnetic core by the winding. A current transformer characterized in that: (2) The current transformer according to claim (1), wherein the two ferromagnetic cores are ring-shaped and coaxially arranged. (3) the two ferromagnetic cores have substantially the same inner and outer diameters and are juxtaposed, and the winding fed by the amplifier forms a coil through which at least a portion of each ferromagnetic core passes. A current transformer according to claim (2).